In communication systems, a method of restricting communication performed by each terminal in accordance with a continuous available call time based on a flat-rate voice service, a cumulative data communication volume based on a flat-rate packet service, or the like is performed.
By the way, when communication systems having the flat-rate voice service as the basic plan become the mainstream, users who hardly use a voice call do not often reach a usage enough to receive the benefit of the flat-rate voice service. Further, when communication systems having the flat-rate packet service as the basic plan become the mainstream, users who hardly use data communication do not often reach a usage enough to receive the benefit of the flat-rate packet service. In this case, the users are likely to have a sense of unfairness about a contract rate of the basic plan.